SPE/IADC 97282

Expandable Sand Screens Selection, Performance, and Reliability: A Review of the

Copyright 2005, SPE/IADC Middle East Drilling Technology Conference & ExhibitionThis paper was prepared for presentation at the SPE/IADC Middle East Drilling TechnologyConference & Exhibition held in Dubai, U.A.E., 1214 September 2005.This paper was selected for presentation by an SPE/IADC Program Committee followingreview of information contained in an abstract submitted by the author(s). Contents of thepaper, as presented, have not been reviewed by the Society of Petroleum Engineers or theInternational Association of Drilling Contractors and are subject to correction by the author(s).The material, as presented, does not necessarily reflect any position of the SPE, IADC, theirofficers, or members. Electronic reproduction, distribution, or storage of any part of this paperfor commercial purposes without the written consent of the Society of Petroleum Engineers orthe International Association of Drilling Contractors is prohibited. Permission to reproduce inprint is restricted to an abstract of not more than 300 words; illustrations may not be copied.The abstract must contain conspicuous acknowledgment of where and by whom the paper waspresented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A.,fax 01-972-952-9435.

AbstractExpandable sand screens (ESS.) are a relatively new sandcontrol system, which combines many of the properties ofgravel packs with the ease of installation of a stand-alonescreen. Although they have been used in a wide variety ofapplications, they are not considered a panacea and have anoperational envelope, which is becoming clearer with time.Weatherfords ESS system currently (June 2005) has 340installations and over 700 years of combined production. Arecent survey of the installations was analyzed in terms ofperformance and reliability.The productivity performance of the ESS has been shownto be very good, with an average skin of 0.3 being achieved inrecent openhole applications. ESS completions generallyperform better than the baseline models. Where fieldcomparisons were possible, they also performed better thanalternative sand control completions.Over the 340 ESS wells, ESS has a reliability comparablewith other sand control systems, with initial failures less than5% and a production failure rate of 0.021 failures/well.year.This gives a projected survival rate at 20 years of greater than90%. This rate is expected to get better with improvingoperations, designs, systems and application selection.IntroductionWhen the first ESS was launched in 1999 it was a radicaldeparture from convention, it introduced the concept of directscreen contact with the formation as a means of increasingproductivity, sand control and reliability.ESS was designed and aimed specifically at openholeapplications, despite the subsequent use of it in cased-holeapplications. Features such as large exposed filter area andvariable ESS borehole contact (becoming known as compliant.

Registered Trademark of Weatherford in the UK

expansion) were included to provide gravel pack functionality

with the operational simplicity of a stand-alone screen. ESShas been used to replace openhole gravel packs (OHGP),cased hole gravel packs (CHGP), cased hole frac and packs(CHFP) and standalone screens (SAS).The design premise was that a compliantly expanded filterthat could eliminate as much of the annular gap as waspracticable would also promote rapid formation stabilizationand minimize the movement of sand particles around thescreen during initial transient sand production period. Thelarge directly exposed filter surface was designed to minimizethe pressure drops in the screen and sand pack compositecaused by mud particles and formation fines. Both featureswere aimed at improving productivity and reliability of thesand-face completion1. The role of the reduction in theannular gap in increasing completion reliability has beendiscussed in Helland et al2.With 340 ESS installations and 65 km now installed, thestatistics are becoming significant and it is now possible withconfidence to determine whether ESS does indeed offer theimprovements claimed by the designers and to formulateselection criteria for their use. This paper presents data onperformance of ESS completions together with data on longterm reliability and failure rates. The ESS applicationselection process is used to show how failure rates can bereduced and long-term reliability improved.ESS PerformanceThere have been a large number of case studies publishedwhich have looked at ESS performance, in a wide variety ofwell types, vertical, horizontal, gas, gas-condensate, water andoil wells. The current maximum fluid production rate is25,000 bpd, the maximum gas rate is 290 MMscf/d, and themaximum water injection rate is 40,000 bwpd. Some specificpublished examples are given below.Weekse et al3 documented the installation and performanceof three long horizontal gas wells in the Brigantine field, in theSouthern North Sea. The wells had up to 40% improvedproduction over expectation. They were completed 32 daysahead of schedule with a saving of $13.5M. These wells havebeen producing for over 4 years.The performance of the ESS completed wells in the gascondensate Scoter Field was also very good with no evidenceof mechanical skin or formation damage4. These wells havebeen producing for over two years.The Xijang Field in China is a mature field with high watercut. The ESS was fitted to a number of wells including a

SPE/IADC 97282

Customer Supplied Openhole Skin Data

40

# Cone OH Skin# Compliant OH Skin

35

# of skins

30252015105>9

>8

>7

>6

>5

>4

>3

>2

>1

>0

>-1

0Skin Value (Range)

Figure 1 Compilation of Openhole Skin Values for Compliant and

Non-compliant ESS

There is as interesting split between applications expanded

with a fixed cone, which will not be fully compliant andapplications expanded with a compliant expander, which willbe generally fully compliant. The non-compliantly expandedapplications have an average skin of 2.3. The fully compliantapplications have and average skin of 0.3. This shows theperformance benefits of compliant expansion. The reason forthis may be due to the compliantly expanded ESS stabilizingthe formation and limiting formation movement and yield.This could theoretically lead to a slightly lower skin18.

Filtercake cleanup and mixing with failed formation material

will also have a large role.Figure 2 shows the openhole skin values broken down forvertical (<15), deviated (>15 & <85) and horizontal (>85)wells. The data shows no negative bias towards the deviatedand horizontal wells, which suggests that the skins are in facttrue formation/completion skins.Openhole Customer Skin Data Analysis

15.00

40

Data WellsAll OH Skins10.00

30

5.00

20

0.00

10

-5.00

# Data Wells

Skin Value

ConeHorizontal

CompliantHorizontal

All Horizontal(>85)

Cone Deviated

CompliantDeviated

Cone Straight

All OH Deviated(<85)

CompliantStraight

All OHstraight(<15)

multilateral5. Each lateral produced two to three times more

than the alternative sand control completions, which were fracand pack and gravel packs.Due to its small running outside diameter and large finalinside diameter (ID) the ESS is particularly applicable tosituations where reductions in final ID must be avoided, suchas in workovers and sidetracks. Oluwatosin et al6 show thatESS completed sidetracks produced between 60-99% morethan the predicted rates.There have been many others, which have noted increasedproduction and a reduction in costs7,8,9,10,11. ESS has alsobeen used as replacements for single and multi-zoneCHGP12,13,14. There have also been theoretical papers, whichhave shown the benefits of the large ID of the ESS inimproving sweep efficiency and the recovery factor of areservoir15.All the references cited above have looked at theperformance of the ESS completed wells shortly afterinstallation. Typically a well test will be performed just aftercompletion to determine the wells performance and to check ifany further clean up or stimulation is needed for the well toachieve its potential. A number of operators have shared theskin values determined from the well tests. Data is availableon 98 wells; some of this data has already been published16.Figure 1 shows an updated compilation of the openhole skinvalues. Although we have no control on how the skins arecalculated, we have been assured that they areformation/completion skin values as defined by VanEverdingen and Hurst17, the effect of deviation and horizontalwells has been removed. The data show that for the openholewells there is an average skin of 0.9. This is a very low valueand compares favourably with other openhole sand controlcompletions.

Figure 2 Openhole skins for vertical, deviated and horizontal wells

The oldest ESS completed wells have now been producing

for close to six years. Case studies are now being publishedlooking at long-term performance (Mason et al19). This casestudy analysed the long-term performance of an installation inQ4 2000, which has now more than four years of productionhistory. The ESS was compared to a SAS and an OHGP inheterogeneous unconsolidated sands. The ESS had muchhigher productivity and lower skin. Also the ESS appeared tomaintain a low skin over the study period, whereas the SASbecame rapidly impaired. The OHGP also declined but to alesser extent. Normally in a sand prone environment electricalsubmersible pumps (ESP) need changing regularly, but thewell with ESS has had the same ESP for more than four years.This is a strong testament to the long-term sand integrity of theESS.To summarise the production performance of the ESS: thepublished data shows that the ESS if correctly applied giveshigh productivity or low skin wells, which maintain theirproductivity over time. Where equitable comparisons aremade, the ESS is better and often much better than thealternative sand control completion option.Production performance is not the only selection criteriaused in choosing the type of sand control to fit to a well.Long-term reliability is also very important.

SPE/IADC 97282

ESS Reliability and Failure Rates

An understanding of reliability and failure rates is central tothe design of any system. There has been a recent survey byKing et al20 published in 2003, which studied the reliability ofa wide range of sand control completions; SAS, OHGP,CHGP, CHFP and ESS. The failures were split into fourcategories: design failures, such as errors in sizing; applicationfailures, which in the context of ESS relates to mechanicaldamage; infant failures defined as failures within 30 days ofthe start of production and production failures, which werefailures after 30 days of production. The first three failurecategories can be classed as initial failures. The data from thepaper is shown in Table 1.TypeofCompletionSASOHGPESSCHGPCHFP

No.ofWells

Well.Years

Designfailures(%)

183175194369844

78350725515143369

0.60101.69

ApplicationFailures(%)09.732.22.4

Infantfailures(%)

ProductionFailures/well/yr

0.60.5710.80.24

0.0560.0200.0160.0110.004

Table 1 Reliability Summary from SPE 84262

The data shows that ESS has similar reliability to OHGP,

and CHGP both of which it typically replaces. Since thepublication of the King paper, there have been many moreESS applications by Weatherford. Weatherford maintains adatabase of all ESS installations in which is captured a widerange of data including failure information. The database isfrequently updated by contacting operators to determine howthe wells are performing. A survey was performed recently bysending out simple questionnaires on each installation. Thisresulted in an update on > 90% of the wells. Using thisinformation we are able to provide up to date statistics onperformance, reliability and failures. The analysis in thispaper is for installations done up to the end of June 2005.Figure 3 shows the success rates within 30 days ofinstallation. Of the 340 installations, 266 or 78% werestraightforward installations, 55 or 16% had NPT (downtime)or required some remedial actions. Eighteen wells (5.6%) wereeither recompleted, sidetracked or abandoned and one wellwas completely lost. The last two categories would be failuresin the King publication.Installation Categories

Loss of Well 1

Combined Initial Failure Rates

Statistics on failure rates as of end June 2005 are shown inTable 2. They show that there have been 340 installationsproducing for a total of 727 years. There have been nineteenwells or 5.6%, which were failures during installation orshortly after the start of production. Of these five were initialdesign failures, due to the weave selection being based onpoor data, of these one may have had some additional screendamage. Two of these design failures have been discussed ina recent SPE paper19. One of the others resulted in the onlyinstallation that to our knowledge resulted in a complete lossof well.Nine installations were classed as application failures, witheight due to parted connections and the other due to screendamage passing through a poorly dressed window. Theconnectors have since been redesigned and have experienced a100% success rate so far.There have been two wells, which could be identified asinfant failures. One a high rate gas well which sanded upimmediately on initial startup, the other a low rate oil well,which also sanded up. In the gas well, there was a largewashout under the casing shoe over which the ESS was run. Itis likely that there would have been a large concentration offlow at this point, which could have lead to rapid erosion.This failure could also be considered as a design failure. Thecause of the other infant failure may have been damage at thetop of the screen but this has never been clearly resolved. Inboth of the infant failure cases, running blank pipe over the topsections could have prevented the failure.Of the nineteen failed wells, three others fell outside thesecategories. One oil well produced 100% water. The twoothers produced sand because the packers were set below thetop of the perforations. These applications were in no way anESS failure. There are two other recent problem wells whichare still under investigation but which are also not ESSfailures. So in reality there are sixteen ESS applications,which failed at or shortly after installation, this is a combinedinitial failure rate of 4.7%.Number of installationsNumber of well yearsDesign FailuresApplication FailuresInfant FailuresProduction Failures

Table 2 Failure Statistics as of June 2005

Sidetrack orRecomplete

18

Remedial Action

19

UnplannedDowntime

36

Operationallystraightforward

2660

100

200

Figure 3 ESS Installation Statistics

300

Figure 4 shows the combined design + application + infant

failure rate as a function of time. Between 2000 and 2002,the failure rate increased until in 2002 there was adisasterously high failure rate of 10% or 8 out of 80installations. The reason for this increase in failure rate wastwofold. As the technology became more accepted, it wasapplied to ever more demanding applications, with the screenproduction rate having to increase dramatically to keep upwith demand. These two conditions combined to give the high

SPE/IADC 97282

failure rate in 2002. The most common failure mode in 2002

was parted connectors, mostly in the 5 size.As a result of this the 5 ESS was withdrawn from themarket.Investigation showed that quality issues hadcombined with a relatively weak connector design (Mark I) tocause failure under certain extreme conditions. The connectorwas redesigned to make it much more robust and underwentextensive qualification testing (Mark II) and since thisredesign there have been no Mark II connector failures.Manufacturing quality control and inspection were alsomodified and improved.These measures have dramatically reduced the combinedinitial rate to less than 2% average over 2003 2005. Thiscorresponds to three wells, one of which sanded up with sandthat was all less than the aperture of the weave. In this casethe weave sizing had been based on inappropriate data. Alsothere was one well in which the old 5- ESS with therelatively weak connector was run (against Weatherfordsrecommendation). This failed due to a parted connector. Inthe third, the ESS was installed incorrectly and did not fullycover the perforations.12.0%

Design+application+infant

10.0%

8.0%

6.0%

4.0%

2.0%

0.0%1999

2001

2003

2005

Y ear

Figure 4 Combined Design+Installation+Infant Failure Rate with

Time

The improving reliability of ESS as shown in Figure 4 is

also due to improved candidate selection and planning. Thisprocess is discussed later in the paper.

Production Pe rform ance

6%

Initial FailureProducing at or aboveexpectation

73%

2%

Not Connected

5%

Depleted

9%

Producing non-optimally

6%

Well shut-in (some issue)

0%

20%

40%

60%

80%

100%

Figure 5 Status of All Installations

Production Failure Rates

Figure 5 shows the current status of all 340 ESSinstallations. As described in the previous section around5.6% of the wells were not produced, of which 4.7% could beconsidered to have failed. 73% are producing at or aboveexpectation. New wells take some time to be connected up topipelines so 2% are not currently connected. Reservoirsdeplete or water out, sometimes unexpectedly quickly so 5%are shut in due to depletion or high water cut. 9% areproducing non-optimally, either poor productivity, restrictedaccess or high fines.Twenty-one of the wells (6.2%) are shut in due to someissue. The primary reasons as far as it can be determined forthe shut-ins are shown in Figure 6. There may have beenmultiple problems in a well but only the primary cause isnoted.The most common is sand production with grains greaterthan the weave aperture. Nine wells are shut-in for thisreason. Three wells were shut-in due to restrictions at acollapsed section of the ESS. Three wells were considerederosive failures; these were cased hole applications.Two other wells also produced sand, but were not thoughtto be ESS failures. One of these wells had a failed frac-pack,and in the other, the sand is thought to have been producedfrom damage in the completion above the ESS.Two more wells were shut-in due to poor productivity.Both of these were cased hole applications and the poorproductivity was thought to be due to perforating issues.Another two wells were shut-in for non-ESS relatedissues; one due to a failed subsurface safety valve and theother due to an underground blowout in a nearby well.So of the original 21 shutins, 15 are directly due to the ESSand 2 others involved sand produced from nonESScomponent of the well. Whether the last 2 failures should beconsidered as ESS failures or system failures is arguable.These 15-17 failures equate to a value of 0.021-0.023failures/well.year depending on whether the non-ESS sandproduction is included. This value is slightly higher than thevalue quoted in the King paper, but very similar to the OHGPfigure.

SPE/IADC 97282

Hydraulic CollapseFormation Collapse

32

Low Productivity other

0

Low Productivity ESS

High Sand non ESS

High Sand Erosion

High Sand > w eave

2

No ESS Issue0

10

Figure 6 Reasons for Well Shut-ins

One other well is under investigation, for a non-ESS

problem, this has not been included in the analysis.With the benefit of hindsight, improved design andapplications screening could have prevented most of thesefailures.Most of the wells with high sand production employedfiltration weave sizes that were based on non-fullyrepresentative sand sieve data. This is a common problembecause accurate data on the sand encountered in a well isonly really available after the well has been drilled. High sandproduction through the weave could have caused erosion and acomplete loss of sand control. High solids production couldalso stop the formation of a stable arch around the wellbore.This could cause transfers of large loads to the ESS, causing itto deform, sometimes severely.Staying below critical velocities by changing productionrates, hole angle or perforating strategies could easily haveprevented the three erosive failures.With recent geomechanical experiments results andpredictive software, weak and collapsing formations can beeffectively predicted and the offending sections isolatedbehind blank pipe.The design and application screening process is discussedlater.Figure 6 also lends credence to one of the principalbenefits of an expandable sand screen, namely the eliminationof plugging or loss of productivity tendencies associated withconventional sand control. It appears that eliminating theannulus and stabilizing the formation reduces the tendency ofthe formation to produce fines, and even when fines areproduced, they flow through the metal weave and hence do notplug the screen. It is perhaps too early to claim this as aproven benefit of compliance, but the indications are good.Long Term Reliability and Failure RatesGravel packs and screen only completions have long casehistories, which allows an evaluation of the long-termreliability of these completion options. ESS has less of a trackrecord due to a relatively short six year run history. Thefailure rate of the ESS is 0.021 per well.year, this is verysimilar to the rates reported in the King et al paper forOHGP17.

One of the parameters that must be known to have a

reasonably accurate field development plan is the probabilityof a well extending the design life of the field. This can beestimated by plotting the failure rate over time. Sand controlcompletions tend to have a relatively rapid failure rate to beginwith then the rate falls off with time. Although there is sparsedata, this can be seen in the failure rate of the ESS wells.There is more in the first year of production than in the secondyear for example.Figure 7 shows the fraction of the wells still producing as afunction of time on a semi-log scale. The plot was generatedusing the failure times for each of the failed wells. The graphshows that the data is falling on a straight line, which suggestan exponential decay in failure rates.The data could be used to project the survival rate of thewells out to say 20 years. This predicts the survival rate after20 years is still greater than 90%.

1.05

1Fraction Still Producing

Re as ons for Shutins

0.95

0.9

0.85

0.80.10

1.00time (Years)

Figure 7 Times to Shut-in for the Failed Wells

10.00

SPE/IADC 97282

ESS Application Qualification Process.

Absolutely fundamental to a reliable completion performanceis the application qualification process. This process isenshrined in Weatherfords Operations Project ManagementSystem (OPMS) software. OPMS is used to manage ESSinstallations from the first meetings with clients to finalinvoicing. OPMS has gates which cannot be passed unless acomponent of the qualification process has been satisfactorilycompleted.In the context of ensuring fit-for-purpose design the OPMSaddresses eight key aspects, which are listed below. Theimportant point is to be aware of these factors so they can beallowed for at the early design stage.1.2.3.4.5.6.7.8.

Hole qualityWell trajectory for deployment and expansionWeave selectionMud selectionBorehole/ESS stabilityMetallurgyErosionFinal clean up and bean up

Long horizontal sections at the end of extended reach wells

can make deployment and expansion difficult. Rejigging thebottom hole assembly and adding drill collars at key locationscan often resolve difficulties. Even if the T+D modelingshows the ESS can be successfully installed, there aresometimes problems during the actual expansion. These canusually be resolved by altering the expansion string, or byusing friction reducing agents.Filter Media Selection ProcessExtensive work has been performed on the performance of thefiltering characteristics of the Dutch twill weave filtrationmedia used in the ESS21. Lab tests measuring retention andpressure build-up on ESS weaves with various reservoir sandshave been in progress since January 2002. The results of thesetests indicate that there is a good correlation between thelargest particles in a distribution and the retention performanceof the weave, i.e. the size of the d10, d5 or d1 of the sand.Figure 8 shows the correlations between sand passing throughand the size of sand in terms of d10 for the 150 micron weave.

4.0

Well Trajectory for Deployment and Expansion

In a given application it is essential the ESS can be safelydeployed and expanded. This process is a function of the welltrajectory and the weight of the string.Prior to every application detailed torque and drag (T+D)modeling is done to ensure that the ESS can be deployed andexpanded safely and without damage. This is usually astraightforward process, but there are circumstances that canprove difficult.

3.5sand passed through (g)

Hole QualityHole quality is important in all types of sand controlcompletions. It includes several aspects such as how in-gauge,and free from tight spots is the hole. Also cleanliness, with theremoval of cuttings beds and thick filter cake recommended.The production and sand control performance of the ESStends to be higher in a gauge hole where compliant expansionis possible or where a fixed cone can be sized to minimize theannulus18. Drilling a gauge hole for a given application isdown to a combination of proper BHA equipment selectionand configuration, Drill In Fluid [DIF] selection and adoptionof good drilling practices. Once the hole has been drilled thenrunning a caliper, either LWD or wireline, can quantify holequality.Hole cleanliness can be managed with proper attention todetail with the drilling fluid to ensure proper cuttings removal.Also prior to running the ESS the drilling fluid must beconditioned at high circulating rates to allow it to pass thefilter weave and to leave the reservoir section with a thin filtercake.Final hole quality can be checked by a slide trip from theprevious shoe to TD. This will also give an up to datemeasure of the friction factors for input into the torque anddrag simulations which are updated immediately prior torunning in hole and real time to verify a problem free ESSdeployment and expansion process as below.

3.02.52.01.51.00.50.00

50

100

150

200

250

300

350

400

450

500

550

600

d10 of sand

Figure 8, 150 micron weave: D10 correlation

Where the d10 of the sand is greater than the weave aperture(150 micron in this case) very little sand passes through theweave. As the sand gets smaller with d10s less than the weaveaperture the amount of sand passing through the weaveincreases gradually at first then more dramatically and therecomes a point where the sand is too small to form a stablefiltercake on the screen. Defining the cut off point foracceptable solids production is difficult, but Hodge et al22proposed a limit of 0.12 lbs/ft2, which correlates to 0.4g sandin these plots. Using 0.4g as the limit for sand production, itcan be seen from the graph that a 150 micron weave wouldgive adequate sand retention for sands with d10s as low as 130micron. The plot of the d5 of the sands against sand passingthrough the 150 micron weave shows that a d5 of 150 micronis just within the maximum area of retention (Figure 9).

SPE/IADC 97282

32.521.510.500

50

100

150

200

250

300

350

400

450

500

550

600

d5 of sand

Figure 9, 150 micron weave: D5 correlation

These experimental results indicate the boundaries of

retention, knowing these is essential for weave sizing. Theweave is sized on the finest sand likely to fail rather thanaverage sand. Knowing that good retention is achieved when5% of the sand is larger than the weave aperture means thatthe coarsest weave able to retain the sand can be selectedenabling easier mud flow through when the screen is run inmud. There are instances where more caution in weave sizingis advisable: for instance when particle size data is limited andif the sands have very high fines contents, or are bimodal.Enough retention tests have been performed to be ablecompare the distributions of potential applications to the sandsalready tested, any that are unsual (for instance bi-modal) aretested. Although sizing according to the d5 of the sand willgive the maximum retention, there can be some flexibility insizing which is helpful for reservoirs with wide variations insand sizes.Mud SelectionOne common concern with the ESS in open hole is thepotential for the mud filtercake to plug the screen whenproduction is first started. With the ESS fully expanded againstthe borehole wall, the mud filtercake will have to be produceddirectly through the weave of the screen. Laboratory tests andfield experience suggest that filtercake flow back is not acommon problem, and Weatherford generally advocatesdesigning the mud in the normal way to ensure hole stabilityand minimal formation damage prior to performing filtercakeflow back tests on the recommended ESS weave.The filtercake lift-off testing takes the form of a core flood,which is done at reservoir temperature and the desired mudoverbalance pressure. The mud is placed dynamically, whichgives a more realistic filter cake and filtrate leak-off, andpermeabilities are measured to oil with the core conditioned toresidual brine. A shroud section and weave disc is pressed intothe mud cake and the permeability to oil is then re-measuredin the production direction. These tests are performed on anoutcrop sandstone since they are designed to identify problemswith the screen rather than formation damage within the rock.A low return permeability will require a baseline test withoutthe screen to check that damage to the core is not responsible.In addition, if the ESS is to be run in the drill-in fluid, mudconditioning will be required to ensure the mud will passthrough the screen without plugging, and laboratory tests maybe necessary to identify the level of solids control required. In

Borehole/ESS StabilityNew operators are sometimes concerned that the relativelymodest ESS strength will cause problems with hole collapse.A simple geomechanical model was developed to betterunderstand the processes leading to excessive deformation andto be used as a screening tool.The model is based on concepts developed fortunnelling23,24 and tunnel support. It calculates the depth of afailed or yielded zone around a wellbore as a function ofwellbore support from a mud overbalance or an expandablesand screen. The yielded zone grows as the mud support isremoved and the well is drawndown and depleted. Volumechanges in the yielded zone compress the ESS.The EWBS model predictions have been calibrated againstexperimental and field measurements of ESS deformation.Figure 10 shows the input/output sheet for the model. Themodel uses various inputs, depth, formations stresses,reservoir pressure, well trajectory, rock properties, anddepletion/drawdown. The model calculates the maximum ESSdeformation during field life. A detailed description of themodel is available.18

sand passed through (g)

3.5

these tests the drilling mud is flowed through the ESS weaveat a constant rate and the pressure drop across the weave ismonitored with time. If 500 mls of mud can pass the weavewithout significant rise in pressure the test is deemedsuccessful. The drill in fluid is conditioned throughincreasingly fine sieves until the test is successful, and themesh rating required is recommended for use in the rigshakers. Before the screens are run in the field rigsite mudtests should be performed to ensure the mud is properlyconditioned.ESS has been successfully run with both water and oilbased muds in open hole. The only problems have occurredwith sized salt systems, the particle size of which can bedifficult to control. As a result Weatherford do not generallyrecommend the use of sized salt systems with ESS.

Figure 10 Input/Output sheet of the Geomechanical Model

0.04000

MetallurgyThe selection of materials for the constituent components ofESS encompasses an evaluation of four main attributes;suitability for expansion without tearing at achievable loads,mechanical strength, fabricability and resistance to corrosion& environmental cracking.A material with a high strain-hardening exponent willpromote uniform plastic deformation to high strain levels andwill be suitable for slotted expandable applications. Fracturetoughness is important to prevent tearing at stressconcentration features, i.e. the slot ends. Solution annealedUNS S31603 (316L) austenitic stainless steel is utilised for thestandard ESS basepipe, weave and shroud and offers highductility, strain-hardening rate and fracture toughness. Otherhigher specification materials such as UNS S32760 (25 Cr),and UNS N08825 are also suitable from an expansionperspective.A secondary aspect of suitability for expansion influencedby material characteristics is the force necessary to generateexpansion. To enhance the strength of the system, it ispossible to increase the basic cross-sectional area, the systemdesign or the yield strength of the material. However, as aconsequence of improvements in mechanical performance,e.g. tensile load bearing capacity or collapse resistance, thereis a concomitant increase in expansion force requirements.This must be assessed against expansion tool loadingconstraints for the length of a specific installation or thegeneric tool design life.The two main mechanical service requirements of the ESSsystem are 1) the capacity to support both the string weightand the axial force component of expansion and 2) to resistcollapse from formation stresses. The weight of the string iscarried by the basepipe through the connections. Theconnection, being more restricted on cross-section by design,has a higher strength requirement than the basepipe.Therefore, solution annealed UNS S32760 or S32750 superduplex stainless steels, possessing a specified minimum yieldstrength more than double that of the austenitic basepipe, hasbeen adopted in the standard ESS product. This materialmaintains good ductility and high fracture toughness at thisstrength level.The original selection of stainless alloys for standard ESSstemmed from a requirement to provide resistance tomoderately-corrosive CO2-bearing reservoirs. Use of a 316Lfiltration medium is common in traditional screenconstruction.An assessment of well corrosivity and a specific materialrecommendation is typically conducted for all ESSapplications. For production wells the fluid, temperature andpressure data is firstly assessed to determine the partialpressures of acid gases and estimate the potential in-situ pH ofproduced waters. The in-situ pH, pH2S, chloride content andtemperature levels are then assessed to evaluate the risk oflocalized corrosion or environmental cracking. Particularattention is paid to the weave material, given the nature of thecritical dimensions in a filter component, and stricter selectioncriteria applied.In cases where well conditions are deemed to present toogreat a risk of weave corrosion failure, an upgrade fromUNS S31603 to UNS N08825 is recommended to enhance the

SPE/IADC 97282

resistance to corrosion and cracking in more aggressive

conditions.Life cycle fluid exposure also plays a role in materialsselection for ESS. Brine and acidizing fluid exposure testshave been performed to evaluate the effectiveness of inhibitingagents and the overall resistance of materials utilized.In one case, sour and corrosive production conditionscombined with a severe acidising program necessitated thedevelopment and installation of a nickel alloy ESS system.The filtration medium was first upgraded to UNS N08825. Tomaintain expansion characteristics, UNS N08825 was alsoused for the basepipe and shroud materials. This gradeexhibits mechanical behaviour similar to UNS S31603. Theequipment was successfully installed with no significantdifferences from a standard installation.In water injection applications, whether seawater,produced or commingled waters, a risk of corrosion exists.This is largely dependent on the control of oxygen levels bystripping and chemical additions. Other factors includeexposure temperature, chloride content, CO2 in gas-strippedsystems, residual chlorine levels and microbiological species.The quality of injected fluid is therefore controlled by theoperator and ESS material selection is based upon reportedfluid control capabilities and control measures.In general terms, the minimum metallurgy recommendedfor permanent completion jewellery in water injection serviceis super duplex stainless steel, particularly where seal surfacesare concerned. In applications with a high level of control,e.g. maintaining <20ppb residual oxygen, there is a potentialfor use of standard ESS materials. However, given the natureof the ESS construction and the abundance of natural crevices,an upgrade of weave material to UNS N08825 orsuperaustenitic material is typically recommended for suchapplications.In more critical or severe water injection applications,other materials have been utilized to enhance resistance tolocalized corrosion. In one instance, the weave material wasupgraded to UNS N06625, with the remainder of thecomponents subject to PREn (Pitting Resistance Equivalentnumber) based selection. This allowed the use of standardconnection material subject to a higher minimum PREnrequirement. To maintain the suitability of basepipe andshroud materials for expansion, UNS S31254 andUNS N08367 superaustenitic stainless steels were selected toprovide enhanced corrosion resistance whilst preservingmechanical performance.The selection of appropriate materials for mechanical andenvironmental application requirements is an importantcontributory factor in the prevention of ESS failures. Theselection philosophy adopted by Weatherford has beendemonstrated by the high success rates enjoyed by the ESSproduct line. To date, no failures relating to corrosion ormechanical performance within the design envelope have beenattributed to the materials of construction.

SPE/IADC 97282

ErosionErosion is usually only a problem is cased hole applications.In a cased hole ESS application, a high flux from theperforations can lead to erosion and a loss of sand control.The ESS has been extensively tested to understand thecontrolling factors and limits on erosion.Over thirty erosion tests have been performed at the SouthWest Research Institute in San Antonio. These tests haveenabled the development of a model which can predict thespecific mass loss as a function of particle size, concentration,type and rate. The specific mass loss is loss in grams from theESS per gram of solids impinging on the weave. The sandintegrity of ESS weave with various percentages of weightremoved was also measured. This allows the approximatetime to failure to be calculated for a given application.For a given production rate the failure times are mostsensitive to the area open to flow. This is due to the specificerosion being proportional to velocity to the power of betweentwo and four. The sand loading and the weight loss at loss ofsand control have a much lesser effect on the time to failure.If in a given application erosion is becoming a concern,then perforating with more shots per foot or with bigger entryholes can dramatically extended the time to failure.Bean upIt is of crucial importance to the productivity, reliability andfunctionality of the ESS that it is brought on to initialproduction in a controlled manner. After installation if thewell is rapidly opened then the filter cake will quickly fall off,possibly mix with failed formation material and plug the ESS.A high-pressure drop could then be applied across the ESS,which could lead to severe deformation or collapse failure ofthe screen. Deformation due to mud plugging takes the screenout of compliance with the formation.Once the ESS begins to deform, it can start to restrictaccess. To mitigate against this, generic bean up procedureshave been developed25. These recommend that nodal analysisbe used to determine the FTHP and FBHP as a function ofchoke setting and rate. If a downhole pressure gauge is usedthen the FBHP can be directly measured. If not or if the gaugefails then choke settings and FTHP must be relied upon.The first choke setting must be small enough (e.g. 8 to 1664ths) so that the total drawdown expected is less than 150psi.This means that a drawdown larger than 150psi is unlikely tobe applied to the ESS. The first choke setting should be heldfor fours hours to allow the filter cake to clean up. The 2ndchoke setting is designed such that the increment in drawdownis less than 150psi and so on up to the maximum rate desired.The total drawdown can exceed 150psi after the 1st chokesetting, only the increment in drawdown must be kept below150psi.After the well has been cleaned up, normal bean-upprocedures can be used.

Figure 11 OPMS Checklist

OPMS Checklist and Failure Avoidance

The OPMS process can be summarised as a checklist wherethe components are represented as a traffic light display(Figure 11). The application should proceed only if all theboxes are green.An amber box signifies a slight issue and a red box a majorissue. Effort must be spent converting all the boxes to green.Many of the ESS failures discussed could have beenavoided if the applications could have been more thoroughlyscreened under OPMS. However there are always limitationsin the validity and extent of data made available. Of the initialfailures, eight were due to parted connectors, which have beenfully addressed with a new connector design. Five morefailures were due to sand size distributions being finer thanexpected.One ESS completion was damaged duringdeployment, another failed due to possible collapse at the ETCand one more through erosion failure at the ETC. All of thesecould have been prevented.Of the subsequent ESS failures, nine were due to high sandproduction with grains larger than the weave. Some of thesehad weaves sized in retrospect on inappropriate data. Threewells had restrictions, which were related to formationcollapse, these could have been screened out. Better wellmanagement could also have avoided the three erosivefailures. All the other failures were not really related to theESS, but they could also have been avoided.ConclusionsESS is a rapidly gaining a track record. The track recordshows that from a production performance viewpoint the ESShas a very low skin and out performs other sand controlcompletion types in similar applications.

ESS has comparable initial failure rates and production failure

Combined initial failure rate 4.7%

Initial failure rate is decreasing with time due torevised designs and better practices, currently<2%Production failure are 0.021 failures/well year

10

SPE/IADC 97282

Projecting this gives greater than 90% survival

rate after 20 years although this statistic must betreated with caution. The vast majority of failures are now avoidable ifthe proper data is available and all procedures arefollowed.The single most important aspect is to have good sand sizedata on which to base weave sizing. Resources spentacquiring this data, or having two strings of different weavesize available could lead to a reduction in failures.AcknowledgementsMany thanks to the operators who took the time to supplyinformation and to Weatherford for permission to publish thepaper.NomenclatureBHA = Bottom Hole AssemblyCHGP= Cased Hole Gravel PackCHFP= Cased Hole Frac PackEBC = ESS Bottom ConnectorESP = Electric Submersible PumpESS= Expandable sand screen (Weatherford Trademark)ETC = ESS Top ConnectorEWBS = ESS Well Bore StabilityFBHP= Flowing Bottom Hole PressureFTHP = Flowing Tubing Head PressureMMscf/d=Million standard cubic feet per dayNPT=Non Productive TimeOPMS=Operations Process Management SystemOH = Open HoleOHGP=Open Hole Gravel Packppb = parts per billionpsi = pounds per square inchSAS=Stand Alone ScreenT+D = Torque & Drag simulationReferences1